Slow-Cooker Vegetable & Chicken Meatball Soup

Heat the oil in a large nonstick skillet over medium-high. Add the onions, garlic, salt, and pepper to the skillet; cook, stirring often, until softened, about 6 minutes. Remove 1/2 cup of the cooked onion mixture, and place in a medium bowl; set aside. Transfer the remaining onion mixture to a 5- to 6-quart slow cooker. Stir the stock, carrots, zucchini, green beans, celery, and tomatoes into the slow cooker.

Add the chicken, panko, 1/2 tablespoon of the parsley, and 1 teaspoon of the oregano to the reserved 1/2 cup onion mixture in the bowl; stir gently with a fork to combine. Shape the chicken mixture into 18 (1 1/4-inch) meatballs. Carefully submerge the meatballs into the chicken stock mixture in the slow cooker without stirring. Cover and cook on HIGH until the meatballs are done and the vegetables are tender, about 2 hours and 30 minutes. Stir in the remaining 2 tablespoons parsley and 1 teaspoon oregano. Ladle the soup into bowls, and serve hot.